I found a few possible planets with Dutch populations.
Confirmed Dutch:
-Utrecht, which is a Lyran/Combine/FRR/Ghost Bear planet.
-Zoetermeer, a Lyran/Falcons/Wolves/Horses planet.
Possibly Dutch:
-Kessel, which could be a reference to half a dozen things and nationalities. Lyran/Combine/RotS planet.
-Dieron (might be a bastardization of Dieren), ofc a Hegemony/Combine/RotS planet.
-Hoonaar, might be derived from Hoornar (Netherlands) but could also be Hoonar (Iran), a FedSuns/Malgrotta(lol) planet.
-Flushing (English name for Vlissingen, it's a stretch, but still possible), a FedSuns planet.
I'd say most Dutch are concentrated in the Lyran Commonwealth and Clan OZs, with possible populations in the Combine and Federated Suns. Like the others said, an argument could easily be made for a few Dutch to be found in the Hanseatic League as well.